Zinc dithiophosphates (ZnDTP) have long been used as antiwear additives and antioxidants in engine oils, automatic transmission fluids, hydraulic fluids and the like. Conventional engine oil technology relies heavily on ZnDTP to provide extremely low cam and lifter wear and favorable oxidation protection under severe conditions. ZnDTP operates under mixed-film lubrication conditions by reacting with rubbing metal surfaces to form protective lubricating films. The mixed-film lubrication regime is a mixture of full-film (hydrodynamic) lubrication wherein the lubricating film is sufficiently thick to prevent metal-to-metal contact and boundary lubrication wherein the lubricating film thickness is significantly reduced and more direct metal-to-metal contact occurs.
However, a problem has arisen with respect to the use of ZnDTP, because phosphorus and sulfur derivatives poison catalyst components of catalytic converters. This is a major concern as effective catalytic converters are needed to reduce pollution and to meet governmental regulations designed to reduce toxic gases such as, for example, hydrocarbons, carbon monoxide and nitrogen oxides, in internal combustion engine exhaust emission. Therefore, it would be desirable to reduce the phosphorus and sulfur content in engine oils so as to maintain the activity and extend the life of the catalytic converter.
There is also governmental and automotive industry pressure towards reducing the phosphorus and sulfur content. As the environmental regulations governing tailpipe emissions have tightened, the allowable concentration of phosphorus in engine oils has been significantly reduced with further reductions in the phosphorus content of engine oils being likely.
There is currently great interest therefore in new antiwear additives that contain little or no sulfated ash, phosphorus, and sulfur (SAPS). Such additives could reduce or eliminate the need for zinc dialkyl dithiophosphate (ZNDTP) in lubricating oils. There have been many approaches to solving this problem, though very few antiwear additives contain no sulfur, phosphorus, or metal species. The present invention is directed in part to providing antiwear to lubricating oil compositions by employing a substituted 1,3-dioxolane-4-methanol compound.
1,3-dioxolanes and numerous derivatives are known. They have been used as a solvent for cosmetics, perfumes, paints, plastics, etc. (see U.S. Pat. Nos. 4,861,764; 5,686,098 and US2008/0280997): they have also been used as disinfectants and aerosols and some are stated to be physicologically active (see Chem. Rev, 1967, 67(4) pp 427-440). 1,3-dioxolanes can be stereoactive and many are prepared as intermediates for the preparation of optically active beta-agonists or antagonists (see U.S. Pat. Nos. 4,575,558 and 5,190,876). U.S. Pat. Nos. 4,374,998 and 4,435,315 discloses branched chain olefin and alkyl derivatives of 1,3-dioxolane for use as flavoring and perfume agents. U.S. Pat. No. 3,883,558 discloses alkyl esters of 1,3-dioxolanes for use a flavorant in an aroma composition. For other flavoring and aroma-enhancing agents see U.S. Pat. Nos. 4,262,030; 3,748,334. Acetal esters and ketal esters derived from glycerol and ethoxylated derivatives are known as fuel additives and for use in lubricating oils (see U.S. Pat. Nos. 5,268,007; 5,093,018; 4,792,411; WO 2008/059155 and US 2008/0234152) and more recently for biofuels (WO 2006/084048; US 2008/0293602; US 2009/0126262; US 2010/0094027). U.S. Pat. No. 7,790,909 is directed to metal working fluids containing a 2-alkyl-4,4-dialkyl-1,3-dioxolane.